The benefit of adapting the transmission parameters in a wireless system to the changing channel conditions is well known. In fact, fast power control is an example of a technique implemented to enable reliable communications while simultaneously improving system capacity. The process of modifying the transmission parameters to compensate for the variations in channel conditions is known as link adaptation. An implicit link adaptation technique is hybrid automatic repeat request (H-ARQ). There are many schemes for implementing H-ARQ, standardized as H-ARQ, H-AQR type II H-ARQ type III and subtypes used for retransmitting erroneous data wherein re ion is adapted to the transmission conditions depending on the ARQ scheme used for retransmitting. Another technique related to the category of link adaptation is explicit adaptive modulation and coding (AMC) which requires explicit transmission condition m measurements or similar measurements to select the fitting transmission parameters. Link adaptation is also achievable using adaptive selection of antenna which is for example implemented as multiple input multiple output antenna processing.
Adaptive modulation and coding (AMC) is part of the techniques behind the concept of high-speed downlink packet access and is one of the main features introduced by code division multiple access communication services.
The main benefits of AMC are higher data rates which are available for users in favorable positions which in turn increases the average throughput of the cell and reduces interference variations due to link adaptation based on variations in the modulation and/or coding scheme instead of variations in transmission of power. Up to now, AMC is only applied in downlink shared channel (DSCH) to enhance transmission data rates.
Since large data amounts are not only transmitted from a base station to a mobile device designated as downlink transmission but also from a mobile device to a base station designated as uplink transmission it is necessary to apply adaptive transmission parameters to the mobile device. User data are transmitted from the mobile device to the base station using random access channel (RACH) including fixed modulation. Up to now there is no transmission method or procedure known, respectively, to enhance data rate provided by the RACH for users in favorable positions.
The usage of adaptive transmission parameters requires the measurement of the current transmission conditions. Therefore, the measurement has to be performed in a way which ensures obtaining transmission condition data reflecting the conditions during transmission enhanced by the usage of adaptive transmission parameters.
Transmission optimization methods are known in the field of mobile communications. For example WO 98/18280 discloses a mobile communications system which allows for significantly reducing a period of time which is required for establishing a random access mobile-originated call. During establishing a mobile station transmits a random access frame that includes a preamble and a plurality of fields. An initial random access frame is transmitted in a first slot with an initial power level and subsequent random access frames are transmitted in following slots with a power level being of the initial power level increased stepwise by a power level offset. The random access frames are transmitted until the mobile station receives an acknowledgement from the base station. The acknowledgement schedules the mobile-initiated call.
Moreover, U.S. Pat. No. 6,181,686 discloses a method which relates to the optimization of data transfer modes for transmissions in cellular telecommunication systems. The optimization is based on a controlling of the data transfer rate by the means a downlink quality measurement (performed by the mobile station) and an uplink quality measurement (performed by the base station). The quality measurements are performed during data transmission and in case the quality measurements over- or underflow one or more pre-defined threshold value(s) a decision to change the currently employed data transfer mode is provoked. In case of a decision to change a handshake message procedure takes place to instruct the new data transfer mode selected. A number time slots used for data transmission is adapted such that in conjunction with the new data transfer mode having a different data transfer rate substantially constant overall data transmission rate is obtained.